The present invention broadly relates to an article having an improved wear resistant and corrosion resistant coating thereon as well as the method of forming such composite article and more particularly, to an improved composite article and process of making the article by which a ductile wear and corrosion resistant nickel-chromium-tungsten base alloy matrix is applied having uniformly dispersed therethrough a plurality of primary wear resistant particles in further combination with secondary chromium and/or tungsten carbide crystals.
A variety of wear and corrosion resistant surface coatings have heretofore been used or proposed for use in a variety of applications where a wear resistant coating on a substrate is desired. Such wear resistant coatings of the types previously known are generally of a very hard and brittle structure rendering them susceptible to stress cracking during application and subsequent service. Such prior art wear resistant coatings are further characterized as generally lacking uniformity in the distribution of wear resistant particles such as tungsten carbide particles, for example, such that the final coating is of a gradient composition resulting in different wear resistant characteristics at different levels of the coating. This has resulted in variable wear rates of the coating as a result of the necessity of machining the coating as applied to proper dimensional tolerances as well as a progressive wear of the coating during service of the article.
The present invention overcomes many of the problems and disadvantages associated with wear and corrosion resistant coatings of the types heretofore known by providing a coating composition and process for applying the coating to a metallic substrate producing a metallurgically bonded coating which is of a tough and ductile characteristic and which further possesses excellent wear and corrosion resistant properties. The coating of the present invention is further characterized by a relatively uniform distribution of the wear resistant particles through the alloy matrix providing for uniform wear resistance as the coating wears during service and is further relatively devoid of any stress cracks. The coating accordingly, is particularly applicable for applying a ductile wear and corrosion resistant coating on the surfaces of extrusion screws for extruding plastics of various types as well as a variety of alternative wear resistant applications in which a ductile wear resistant coating is desired.